This invention relates to a tank cap for the fuel tank of a vehicle, which seals the fuel tank from the exterior of the vehicle unless the tank cap is opened for the purpose of, for example, adding fuel. More particularly, the invention relates to a tank cap having features which optimize space requirements and which enhance manufacturability and improve the safety of the finished, installed product.
Conventional tank caps for closing the filler neck of a vehicle fuel tank usually include a closure member for closing the mouth of the filler neck and a handle or cap element which moves relative to the closure member to permit a user to install or remove the tank cap. It is known to provide tank caps that can be inserted and removed without having to rotate the cap for through multiple 360.degree. rotations. It also is known to provide a tank cap that is installed or removed with less than a full 360.degree. rotation. This feature not only is convenient to the user, but a tank cap with an angle of free travel that is something less than 360.degree., e.g., a angle in the range of between 90.degree. and 270.degree. and preferably 180.degree., is less likely to become dislodged to expose the fuel tank in the event of an accident when the body of the vehicle is impacted or deformed. Owing to the free travel feature, even when something is forced onto the cap element of the tank cap in a substantially linear movement, the cap element will rotate or give to some degree without the result of dislodging the tank cap from the filler neck of the tank and, thus, a hazard is avoided that otherwise would be presented by escaping fuel. In some countries, automobile manufacturers are required by law to provide tank caps characterized by an angle of free travel.
U.S. Pat. No. 5,794,806 discloses one manner of implementing a free travel feature. This tank cap has a return spring, configured as a torsion spring, between the cap element and the closure element which is attached at its corresponding ends to rotate in unison on the cap element and on the closure element. During assembly of the two components, the untightened return spring initially is inserted into one of the two components and the other component then is positioned on the component into which the spring has been inserted. The spring tension that occurs when the cap element is rotated relative to the closure element is bounded by reason of a first stop, against which the cap element is held, and a second stop, which limits the maximum angle of free travel through which one of the components can rotate with respect to the other.
This implementation of the free travel feature can result in a less than optimum design, however, because in this tank cap the torsion spring is arranged in a plane that is perpendicular to the plane of rotation of the cap element. Thus, the tank cap must be long enough or tall enough to accommodate the length or height of the spring. A tank cap of the type disclosed in U.S. Pat. No. 5,794,806 also can be difficult to assemble and to subsequently inspect. For example, assembly of such tank caps frequently still is accomplished manually, and it is possible for the spring to be incorrectly inserted during assembly, such that the spring force will act in the opposite, and therefore in precisely the wrong, direction.
If an error is made in the assembly of a tank cap of this type, the error can prove to be difficult to detect, because both components nevertheless still are rotatable with respect to each other, albeit in the direction from the second stop to the first stop rather than in the correct direction from the first stop to the second stop. The rapid check that usually is performed in the course of industrial mass production of tank caps is not likely to reveal this sort of error, and the problem is not likely to be discovered until an attempt is made to install the tank cap to seal the filler neck of the fuel tank. Efforts to more thoroughly inspect the tank cap at the time of assembly of the cap element and the closure element would increase the time required for the inspection, as the inspector necessarily not only would have to check whether the cap element is rotatable under a spring load, but also whether the direction of rotation is the proper direction.
What has been needed and heretofore unavailable is a tank cap that is designed to make efficient use of space and can be manufactured cost effectively, that can be installed with the least possible risk of error, and that subsequently can be timely and easily inspected in order to detect any assembly errors which do occur. The present invention satisfies these needs.